IMMUNITY. 301 



was made to secure protective virus (vaccines, 

 lymphs) which should affect the animals but 

 slightly and yet protect them against a subse- 

 quent infection from either artificial or natural 

 sources. 



In 1884 Ferran 1 first protected guinea-pigs 

 against fatal doses of the cholera bacteria by 

 subcutaneous inoculation with the same germs. 

 After Gamaleia had discovered a method by 

 which comma bacilli of constant and high vir- 

 ulence could be obtained, W. M. Haffkine cul- 

 tivated two varieties of different degrees of 

 virulence and with these he carried out in In- 

 dia in 1893-94 protective inoculation against 

 cholera, although with slight success. 2 



Diminution of the virulence of bacteria is 

 especially effected by cultivation with abun- 

 dant access of air, at times in connection with 

 access of light conditions the significance of 

 which in the removal of virulence has already 

 been mentioned on p. 56, by cultivation at 

 high temperatures (p. 66), and by the addition 

 of chemical substances (p. 90). Sometimes it 

 is advantageous to proceed with the attenuation 

 in definite stages in order to obtain virus of 

 different degrees of strength. In the case of 



1 Compt. rend, de 1'Acad. des sciences, CI., 1885. 



2 At the present date Haffkine's results as a whole must be looked 

 upon as distinctly encouraging. E. O. J. 



